Nitrates, RODI water and salt mix

JPK · Dec 19, 2016

I have a quick question about nitrates, RODI water and my salt mix.

I mixed up 25 gallons of fresh salt mix (brand new bucket of AF Reef salt), circulated/aerated/heated it for a few hours and then tested the nitrates of the fresh mix, which was between 1 and 2 ppm (Salifert and Red sea).

I was a little concerned that there may be nitrates in my RODI, since my test kits usually won't register nitrates on the fresh mix.

So I tested my pure RODI (zero TDS) and there were no detectable nitrates. I slowly mixed in salt mix to get to 35 PPT, and then re-tested. The reading was around 1 or 2 ppm nitrates again.

I know 1-2 ppm nitrate is not too concerning. However, I just wanted to verify that the salifert and red sea test kits are accurate when testing freshwater only, since if there are nitrates in my RODI I want to try and figure out why.

Thanks

Jason

Randy Holmes-Farley · Dec 19, 2016

One issue is that a small amount of nitrite can show up as more nitrate.

JPK · Dec 19, 2016

Thanks for the quick reply Randy,
I assume you are saying there may be a small amount of nitrite in the salt mix, or are you referring to the RODI water? Either way, should this be concerning?
thanks
Jason

Randy Holmes-Farley · Dec 19, 2016

JPK said:
Thanks for the quick reply Randy,
I assume you are saying there may be a small amount of nitrite in the salt mix, or are you referring to the RODI water? Either way, should this be concerning?
thanks
Jason

I'm just warning that it may not be that much nitrate. Salt mixes often have ammonia. If some salt water sat around long enough to become nitrite, that might happen, or it might be nitrate in the tap water.

Have you measured the TDS of the RO/DI effluent?

Have you measured the nitrate in the tap water itself?

JPK · Dec 19, 2016

Hi Randy,
I live in So Cal and we have pretty nasty tap water due to the drought.
I just measured the nitrate of my tap water, which is close to 30 ppm. The nitrate of the fresh RODI water, which I use to mix with the salt, is undetectable.
The effluent from my RODI is around 780 TDS, the TDS of the tap water from the tap is around 622. My RODI effluent travels about 35 feet and waters a tree, i assume there is a bunch of gunk in the line.
The TDS going into my DI resin, from the carbon filters, etc. is 22, the TDS coming out of the DI resin is zero.
The salt mix was "mixing" for about 12 hours. However, I made a small new batch which had the same nitrate reading.
Thanks
Jason

Randy Holmes-Farley · Dec 20, 2016

Might be a bit of nitrate getting through the DI, or it may be test error. As long as the TDS stays zero coming out of the DI, the amount will be minimal and I wouldn't worry about it.